Q: I switched my iphone 5 carrier from AT&T to T-Mobile, in doing so, does this now mean that I can't receive updates such as iOS 7?

No

Not unless you did something stupid like hack your phone to unlock it instead of getting it legitimately unlocked by AT&T.

All iOS devices receive the updates at the same time.

Unless your device is no longer supported (Which obviously the iPhone 5 being the most recent iPhone, it isn't), you can always update, almost no matter what. You can even be jailbroken and still receive updates, only it will more than likely remove your jailbreak (Also apple advises you to not jailbreak your device for obvious security reasons)